The present invention relates to a developing device and to a method for developing visible electrostatic latent images formed on a light-sensitive member using an electrophotographic apparatus. More particularly, the present invention relates to a developing device of an electrophotographic machine which developes by using both a developer, such as a one-component magnetic toner powder, and electrostatic latent images.
Conventional developing devices of conventional electrophotographic apparatus have been developed by utilizing a toner charged with polarities opposite to that of the electrostatic latent image on a light-sensitive member. One such developing device is disclosed in S. Nelson, U.S. Pat. No. 4,121,931 entitled "ELECTROGRAPHIC DEVELOPMENT PROCESS" issued on Oct. 24, 1978.
Conventionally and as disclosed in the above U.S. Patent, as the toner is usually charged with a polarity opposite to that of the electrostatic latent image, regardless of whether it is a contact development or a non-contact development, the toner adheres to the non-image region, and thus copies are damaged, especially, they are smeary or are scattered copied images.
This is because charges having a polarity similar to that of an image section remain on a non-image section on the paper at the developing stage. That is, a toner charged with polarity opposite to that of the image section is attracted from a toner supplied on the non-image section on the paper by the remaining charges on the non-image section.